Method for machining with laser beam



1 l 2 1 unuwu Mm n-nmuvm. gnu-mum" nwwm April 22, 1969 R. s. OTSTOT ETAL 3,440,338

' METHOD FOR MACHINING WITH LASER BEAM Filed April 4, 1966 I MASK' l4 LENS LASER HEAD A PROTECTIVE COVER GLASS INPUT POWER WORK PIECE INVENTORS ROGER S. OTSTOT DURWOOD G.BLAND JAMES W. MEEKS AT ORNEY United States Patent 3,440,388 METHOD FOR MACHINING WITH LASER BEAM Roger S. Otstot, Raleigh, and Durwood Gene Bland and James W. Meeks, Durham, N.C., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Apr. 4, 1966, Ser. No. 539,885 7 Int. Cl. B23k 9/00, 15/00, 9/16 US. Cl. 21969 2 Claims ABSTRACT THE DISCLOSURE A method for drilling holes through hard, solid materials, such as steeland tungsten, with a laser includes the improvements of coating the light entrance and exit surfaces of the material with parafiin oil and silicone grease.

The present invention relates to an improved method for drilling holes in extremely hard materials. More particularly, this invention relates to a method for drilling micron-sized holes or orifices in extremely hard and brittle workpieces with a laser ,beam. 1

Although the discovery of the laser occurred only recently, there have been many industrial applications envisioned for this amazing scientific development. One important achievement in the industrial field has been the successful drilling of micron-sized holes in materials such as industrial diamonds and superalloy metals. Heretofore, this laborious and tedipus task has been performedby such techniques as ultrasonic and spark drilling. Perhaps the principal reason why drilling by laser appears to be so attractive is that the pulsed light beam emitted by the laser seems literally to .tunnel its way through the workpiece without its energy becoming dispersed across the surface beyond the diameter of the beam. The graingrowth or fragmentary deterioration which is characteristic of holes drilled with continuous heating is avoided and thus facilitates the drilling of holes approximately the diameter of the focused laser beam itself. Not only can smaller holes be drilled with the laser, but the process can be accomplished in a fraction of the time required by the previously known methods. Both of these feats are explained by the fact that the coherent beam emitted by a laser actually vaporizes the material which it is focused upon.

Unfortunately there are some problems with laser-made holes. It has been found that undesirable results, such as the holes being tapered, the splatter of material around the entrance of the hole, and a raised rim formed around the entrance and exit of the hole, must be corrected in most instances. Therefore, the laser cannot be the complete answer to all drilling problems unless some technique can be provided to obtain holes which do not have to be reworked. If a method could be employed which would eliminate the problems stated above, it would represent an important improvement in the art of laser drilling.

Therefore, it is a principal object of the present invention to provide an improved method for drilling holes with a laser beam. Another object is to reduce the taper of laser-made holes. Another object is to eliminate the splatter of vaporized material around the entrance of laser-made holes. Another object is to reduce substantially the size of the rims around the entrance and exit of the holes. Other objects and advantages will become apparent from a reading of the description of the invention to follow.

The foregoing objects and others ancillary thereto are preferably accomplished as follows:

According to a preferred method for carrying out this invention, the workpiece is prepared for laser drilling by applying a thin film of material on the laser beam entry "ice side .of said workpiece prior to drilling. The exit side of said workpiece iscoated with a reasonably heavy film of material. The surface entry coating should be either a liquid substance having lowsurface tension, or a thin sheet of material such as aluminum foil bonded thereto which may be removed easily after the hole has been made. When using a liquid it is preferable to select one which readily wets the surface to insure that a thin flat film can be deposited which will not affect the focus of the laser beam. The liquid selected should also have a relatively low vapor pressure at a room temperature to prevent a sizable amount of evaporation of the liquid prior to drilling. There are a number of liquids which have the necessary properties, but paraffin oil has proven to be an excellent coating agent for the beam entry side. Quite unexpectedly, when a drop of paraflin oil is placed on the workpiece surface at the point to be drilled, ,the splatter around the entrance of the hole is essentially eliminated and the size of the rim at the hole entrance and exit is substantially reduced. Also the discovery has been made thatwhen the exit surface is coated with a viscous material, such as silicone grease, the taper of the hole is reduced in addition to minimizing the rim on the exit surface. It is theorized that the grease prevents escape of volatile molten material from the exit side, thus forcing this matcrial'to exit through the entrance of the hole causing more material to be eroded or vaporized at the hole exit which increases the exit diameter to reduce the objectionable taper that results when a coating is not employed. After the workpiece has been coated, the holes are made in accordance with procedures which will be explained in detail herein to follow.

This invention provides the advantages of drilling holes in hard and brittle materials with a laser which do not require additional time consuming finishing operations such as machining. and polishing. Laser-drilled holes which have been coated in accordance with this invention are replicas of the patterned light beam employed and the entranceand exit cross sections are essentially the same. For example, when a circular-shaped light beam is employed the resultant holes are substantially round and have essentially the same entrance and exit diameters. The surface coatings of this invention improve the 1aser= drilled holes made in hard metals ranging from brass to the superalloys and especially with the polycrystalline ceramics and single crystals such as industrial gems. The industrial gems include diamonds, sapphires and rubies which have been processed for special industrial applications.

The novel features considered characteristic of the present invention are set forth with particularity in the appended claIms. The invention itself however will be best understood from the following description thereof when read in connection with the accompanying drawing in which:

A single figure shows a side elevational view of a laser drilling arrangement typical of the set-up preferred for carrying out the drilling operations in which the concepts of the present invention are employed.

In the drawing there is shown a laser head 10 which is preferably a solid state pulse laser that is not Q-switched since the longer pulse width of light from a non-Q- switched laser is advantageous in drilling operations. The laser head houses a flash tube and laser rod enclosed in an eliptical cavity, not shown. The head 10 is powered by a power supply 12 capable of delivering enough energy to perform the required driling operation for a particular workpiece. A mask 14 is employed to shape the light beam 16 prior to being focused by lens A and B. In the arrangement shown, the mask 14 is provided with a circular hole 15 to facilitate dri.ling a round hole. A workpiece 18 is positioned with the surface nearest the lens being at the focal point of lens B. Although a double lens arrangement is shown, it will be understood that either a single lens or several lenses may be used, the only restriction being that the last lens nearest the workpiece be the form of intense local heat which actually vaporizes an area of the workpiece the size of the light beam in an instant to provide a hole having a well defined cross section. After the drilling operation has been completed the workpiece is cleaned and examined microscopically to positioned at its focal length from the surface of said check the quality of the newly formed hole. workpiece. A protective glass 20 is posiioned between the The examples listed in the fol'owing tables are repreworkpiece 18 and the adjacent lens B to prevent molten sentative of the holes which can be laser-drilled employing or vapolized material from damaging the lenses. The the methods of this invention. These examples are inprotective glass 20 should be made from a material which 10 tended to be illustrative and are not to be construed as will not alter the effectiveness of the laser light beam. limiting the invention beyond that which is disclosed else- In order to illustrate a specific procedure for demonwhere herein.

Coatings Hole diameter, Effects produced around hole perimeter Type of material (inches) Hole drilled shape Entry Exit Entry Exit Tungsten, .010 inch 006 .002 Much splatten. Much splatter. thick. 006 003 Very little splat Some splatter.

. 006 004 0 do None other than slight slight scorching.

Brass, .005 inch None None .006 .003 Round... Some splatter Some splatter.

thick. Paralfin oil do 006 .0035 do. None other than Do.

. slight scorching. do Silicone grease .010 .007 do. Slight splatter None other than slight scorching.

Beryllium oxide None None .006 .003 Round..- Much splatter, large Some splatter.

ceramic, .011 inch crater. thick.

Parafiin oil do 007 0035 .do. No splatter or crater- Do.

do Silicone grease .005 .004 do do Only slight scorching.

Sapphire (single None None .005 .002 Round.. Large crater Some shattering.

clrystal), .009 inch Paraffin oil do .005 .003 o No crater Do. 1; lie 1 i .do Silicone grease .005 004 do. Verl li little effect at Very clean.

Molybdenum, .005 None N .006 .002 Round Small crater None.

inch thick. Aluminum foil.. Silicone grease. 006 .0045 do No splatter... Do.

Parafiin oil do .006 .004 ..do Slight splatter Do.

Tool steel, .005 inch None None 0035 .002 Round.. Crater of molten Very small ridge.

thick. metal and scorch- .do Silicone grease .0025 .002 do Large crater None.

Paraffin oil do .002 002 .do... Small crater Do.

Tungsten, .005 inch None None .003 .0015 Round... Small crater Small amount of hick. splatter.

.002 .002 None. .002 .002 Do.

Molybdenum, .005 .003 .0015 Round Small crater" Some splatter.

inch thick. 0.... .002 .00175 do Large crater None.

Parsfiin oil .002 .00175 do.--- No crater, some Do.

splatter.

Aluminum oxide None None .003 .0025 Ronni... Large crater Some splatter.

ceramic, .010 inch .002 .002 do do None thick. .0025 .002 ..do. No crater Do.

Ruby (single 0025 002 Round Crater with hairline Some splatter.

crystal), .004 inch cracks on inner thick. wall.

Paraffin oil do .002 .002 do Crater and cracks Do.

practically eliminated.

do Silicone grease .002 .002 -..do No crater Very little splatter.

strating the present invention, the workpiece 18 is coated From the foregoing data it will be appreciated that the on the surface of entry with a thin film of material having 55 method of the present invention substantially reduces the a planar surface which does not affect the focus of the problems encountered heretofore with laser drilling. Holes lenses. The opposite or exit surface is uniformly coated can now be laser drilled with rep oducible accuracy havwith a .dense material such as a grease. The coated workmg a high degree of confidence. The invention is applica piece is then positioned in alignment such that the front ble to drllling and machining of all types where minute surface thereof is at the focal point of lens B and per- 69 amounts of material are removed from materials which pendicular to the common axis of the lenses and the laser ar dlfiicult to work with because of their hardness or beam The mask plate 14 is ositioned between lens A brittleness factor. It has been found hOWCVCI that the illand laser ltead 10 to pattern or shape the light beam 16 as vcntion is particularly advantageous and suitable for drilldesired depending upon the configuration of the hole mg micron-sized holes in extremely hard or brittle matewanted in the workpiece 18. To iniiate the laser beam, 35 T1315 Whlch have 136611 extremely difficult and expensive the power supply capacitors are charged to the approprito dr1.l by conventional drilling techniques. Some specific ate energy level before this stored energy is released by examples are orifices in spinnerets which are employed to a a tu i mechanism t th fl h t b hi h pumps exfrude continuous microdenierfilaments from a flowable the laser rod above its lasing threshold. The foregoing matenal- Another Specific application for Which the la le t are f a ll known t d are t shown 7 venuon is useful is the drilllng of watch ewels. The $1311]- o d ib d i d il, Th coherent b 15 i d b nerets and watch ewels are acceptable for industrial uses the laser rod passes through the aperture 15 in the mask except for a IlOInlIlfll amount of finlshlng Work that can E and to the lens arrangement, A and B, which focuses be accompllshed P Y- the beam on the coated surface. The workpiece absorbs What is claimed is: energy from the coherent light beam and dissipates it in 75 1. A method for drilling holes through hard, solid ma density greater than water.

2. The method of claim 1 wherein the dense viscous medium is silicone grease,

References Cited UNITED STATES PATENTS Browne 219-69 Inoue .1 219-68 Johnson .E hhhh w 2l9-121 Norton mum, 219 121 Roshon et a1 219-121 1 6 4/1967 Becker 219-121 9/1967 Okazakietal 219-121 2/1968 Di Curcio 219-421 OTHER REFERENCES I.B.M. Technical Disclosure Bulletin, S, H, Kremen,

vol. 8, No. 3, August 1965, p. 434.

Laser in Metalworking, R. Microsa, Microtechnic, vol, 29, No. 2, April 1965, pp. 96-99.

10 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner.

US. Cl. X.R. 

